Mix flour, salt, icing sugar, baking powder and ground almonds in a bowl. Add 1 egg and butter. First with the dough hooks of the hand mixer, then with your hands to a smooth dough.
Grease 6 Tartelettes (approx. 10 cm Ø; with lift-off base) and dust with flour. Divide the dough into 6 portions of equal size. Roll out round (13-14 cm Ø) on a floured work surface or press flat by hand.
Line the ramekins with it, press down on the edges and chill for about 15 minutes. Mix sour cream, milk, starch, 2 eggs and 4 tbsp. sugar until smooth. Clean and wash the rhubarb, cut into small pieces and distribute in the moulds.
Pour a sand casting over it. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-25 minutes. Cover with aluminium foil at the end. Remove the tartlets, let them cool down on a cake rack and take them out of the moulds.
Mix jam and 1-2 tablespoons of water until smooth, bring to the boil and spread on the tartlets. Dust with icing sugar.